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Biomedical subjects

R A Demel

Publications and source records attributed to R A Demel.

At least 109 records · Page 6Linked to original sources
PubMed1977

[Preferential affinity of acetylcholine receptor protein for certain lipids studied using monolayer cultures].

The interaction of the cholinergic (nicotinic) receptor protein purified from Torpedo marmorata electric organ with lipidic monomolecular films is studied at constant film area or constant superficial pressure. In both experimental situations, it is incorporated more efficiently into cholesterol than into egg lecithin films without showing any selectivity for a particular phospholipid class.

Acetylcholine↗
PubMed1977

The protein-mediated net transfer of phosphatidylinositol in model systems.

The phospholipid monolayer technique has been used to study the transfer activity of the phospholipid exchange protein from beef brain. In measuring the transfer between a monolayer consisting of equimolar amounts of phosphatidylcholine and phosphatidylinositol and liposomes consisting of 98 mol% phosphatidylcholine and 2 mol% phosphatidylinositol, the beef brain protein demonstrates an 8-fold higher transfer activity for phosphatidylinositol than for phosphatidylcholine. Under similar conditions the phosphatidylcholine exchange protein from beef liver showed a great preference for phosphatidylcholine. Phosphatidylcholine liposomes devoid of phosphatidylinositol still functioned as receptors of phosphatidylinositol when the beef brain exchange protein was present. This indicates that this protein can catalyse a net transfer of phosphatidylinopsitol. Binding of both phosphatidylinositol and phosphatidylcholine to the beef brain protein was shown.

Animals↗
PubMed1977

High performance liquid chromatographic separation and direct ultraviolet detection of phospholipids.

A fast and efficient method for the separation of (phospho)lipids by high performance liquid chromatography using n-hexane, 2-propanol, water mixtures as the solvent system is described. The lipid separation occurs on a LiChrosorb Si-60 (10 micron) column and the individual components are monitored directly by ultraviolet absorption at 206 nm. Of a total lipid extract from erythrocytes a complete separation is achieved of cholesterol, phosphatidic acid, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, lysophosphatidylcholine and lysophosphatidylethanolamine, whereas phosphatidylcholine and sphingomyelin are only partly separated under these circumstances. Furthermore, a mixture of synthetic phospholipids, i.e. 1,2-dilauroyl-sn-glycero-3-phosphatidic acid, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, 1,2-dioleoyl-sn-glycero-3-phospho-1'-sn-glycerol and 1,2-dioleoyl-sn-glycero-3-phosphocholine has been completely resolved. In addition to separation of phospholipids in different classes, separation of molecular species can also be achieved in some cases, as is shown for 1,2-dipalmitoleoyl-sn-glycero-3-phosphocholine and 1,2-didocos-13'-cis-enoyl-sn-glycero-3-phosphocholine.

Animals↗
PubMed1977

The preferential interaction of cholesterol with different classes of phospholipids.

1. By differential scanning calorimetry a preferential affinity of cholesterol for sphingomyelin was established in mixtures of sphingomelin and phosphatidylcholine where sphingomyelin was either the higher or the lower melting phospholipid. 2. A preferential affinity of cholesterol for sphingomyelin was also found in mixtures of sphingomyelin and phosphatidylethanolamine where sphingomyelin was either the higher or the lower melting phospholipid. The sphingomyelin used was isolated from beef erythrocytes or synthetic palmitoyl sphingomyelin. 3. In mixtures of phosphatidylserine with phosphatidylethanolamine, or phosphatidylserine with phosphatidylcholine, cholesterol showed the highest affinity for the lower melting phospholipid. 4. In a previous paper (van Dijck et al. (1976) Biochim. Biophys. Acta 455, 576-588) it was established that cholesterol has a higher affinity for phosphatidylcholine than for phosphatidylethanolamine. The affinity order of cholesterol for the neutral phospholipids which can be deduced form these experiments is sphingomyelin greater than phosphatidylcholine greater than phosphatidylethanolamine.

Calorimetry↗
PubMed1977

Evidence for the preferential interaction of glycophorin with negatively charged phospholipids.

Glycophorin, extracted from the erythrocyte membrane after treatment with lithium-diiodo-salicylate, still contains a significant amount of phospholipid, consisting predominantly of phosphatidylserine. Methods are described which lead to a full delipidation of the protein. After treatment with neuraminidase, delipidated glycophorin shows a preferential interaction with monolayers of negatively-charged phospholipids. This lipid-protein interaction is decreased by the presence of cholesterol in the lipid film.

Animals↗
PubMed1976

The preference of cholesterol for phosphatidylcholine in mixed phosphatidylcholine-phosphatidylethanolamine bilayers.

The following phosphatidylethanolamines were studied by differential scanning calorimetry: 1,2-dipalmitoleoyl-, 1,2-dioleoyl-, 1,2-dilauroyl-, 1,2-dielaidyl-, 1,2-dimyristoyl- and 1,2-dipalmitoyl-sn-glycero-3-phosphoryl-ethanolamine. The saturated and trans-unsaturated species underwent thermotropic phase transitions at temperatures about 20-30 degrees C higher than the corresponding phosphatidylcholines but the enthalpy changes were nearly identical. The transition temperatures for the cis-unsaturated species were about the same as those of the corresponding phosphatidylcholines but here the enthalpy change was markedly decreased as compared with the phosphatidylcholines. Freeze-fracture electron microscopy revealed phase changes from a lamellar to a hexagonal phase for 1,2-dipalmitoleoyl- and 1,2-dioleoyl-sn-glycero-phosphorylethanolamine at 20 and 0 degrees C respectively. At these temperatures no transitions were apparent in the calorimeter scan. Incorporation of increasing amounts of cholesterol into phosphatidylethanol-amine bilayers gradually decreased the enthalpy changes of the phase transition in the same manner as was demonstrated before for phosphatidylcholine/cholesterol mixtures. This was studied both for 1,2-dipalmitoleoyl- and 1,2-dimyristoyl-sn-glycerophosphorylethanolamine. In an equimolar mixture of 1,2-dioleoyl- and 1,2-dipalmitoylphosphoryl-ethanolamine, which showed phase separation, cholesterol preferentially decreased the transition of the lowest melting component. In equimolar mixtures of phosphatidylethanolamines and phosphatidylcholines, which showed phase separation, cholesterol preferentially abolished the transition of the phosphatidylcholine component present. This occurred both in experiments where the phosphatidylcholine was the lowest melting and where it was the highest melting component present in the mixture. These experiments strongly suggest that in phosphatidylcholine-phosphatidylethanolamine mixtures at temperatures where both components are in the liquid-crystalline state cholesterol is preferently associated with the phosphatidylcholine component in the mixture.

Cholesterol↗
PubMed1976

The protein-mediated transfer of phosphatidylcholine between membranes. The effect of membrane lipid composition and ionic composition of the medium.

The phosphatidylcholine exchange protein from bovine liver catalyzes the transfer of phosphatidylcholine between rat liver mitochondria and sonicated liposomes. The effect of changes in the liposomal lipid composition and ionic composition of the medium on the transfer have been determined. In addition, it has been determined how these changes affected the electrophoretic mobility i.e. the surface charge of the membrane particles involved. Transfer was inhibited by the incorporation of negatively charged phosphatidic acid, phosphatidylserine, phosphatidylglycerol and phosphatidylinositol into the phosphatidylcholine-containing vesicles; zwitterionic phosphatidyl-ethanolamine had much less of an inhibitory effect while positively charged stearylamine stimulated. The cation Mg2+ and, to a lesser extent, K+ overcame the inhibitory effect exerted by phosphatidic acid, in that concentration range where these ions neutralized the negative surface charge most effectively. Under conditions where Mg2+ and K+ affected the membrane surface charge relatively little inhibition was observed. In measuring the protein-mediated transfer between a monolayer and vesicles consisting of only phosphatidylcholine, cations inhibited the transfer in the order La3+ greater than Mg2+ larger than or equal to Ca2+ greater than K+ = Na+. Inhibition was not related to the ionic strength, and very likely reflects an interference of these cations with an electrostatic interaction between the exchange protein and the polar head group of phosphatidylcholine.

Animals↗
PubMed1975

Relation between various phospholipase actions on human red cell membranes and the interfacial phospholipid pressure in monolayers.

The action of purified phospholipases on monomolecular films of various interfacial pressures is compared with the action on erythrocyte membranes. The phospholipases which cannot hyorolyse phospholipids of the intact erythrocyte membrane, phospholipase C from Bacillus cereus, phospholipase A2 from pig pancreas and Crotalus adamanteus and phospholipase D from cabbage, can hydrolyse phospholipid monolayers at pressure below 31 dynes/cm only. The phospholipases which can hydrolyse phospholipids of the intact erythrocyte membrane, phospholipase C from Clostridium welchii phospholipase A2 from Naja naja and bee venom and sphingomyelinase from Staphylococcus aureus, can hydrolyse phospholipid monolayers at pressure above 31 dynes/cm. It is concluded that the lipid packing in the outer monolayer of the erythrocyte membrane is comparable with a lateral surface pressure between 31 and 34.8 dynes/cm.

Cell Membrane↗